String Coding Interview Questions In Java
Java Edition
String coding interview questions in Java typically focus on the candidate's understanding of string manipulation, handling different data types, and knowledge of various methods to work with strings. These questions test the candidate's ability to efficiently use string processing techniques, handle edge cases, and write clear and efficient code. The interviewer may also ask about common methods like substring, length, and concatenation, and how to compare strings, reverse them, or check for specific characters or substrings. Candidates may also be asked about string immutability, memory management, and performance considerations while working with strings. Overall, these questions assess a candidate's fundamental skills in Java programming and their ability to solve problems related to strings.
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1 - What is an immutable string in Java?
An immutable string in Java is a string that cannot be modified once it has been created. This means that any attempt to change the value of the string results in the creation of a new string object.
2) How do you create an immutable string in Java?
You can create an immutable string in Java by using the keyword “final” in the variable declaration. This ensures that the reference to the string cannot be changed and therefore the string is immutable.
3) What is the difference between String and StringBuffer in Java?
String is an immutable class whereas StringBuffer is a mutable class. This means that a String object cannot be modified while a StringBuffer object can be modified by using various methods such as append() and insert().
4) Can you create a String object without using the new operator?
Yes, you can create a string object without using the new operator. This is because Java provides a shortcut for creating string objects using string literals, i.e. enclosing the characters within double quotes.
5) What is the use of the intern() method in String class?
The intern() method in String class is used for interning string objects. This means that it checks if there is already a string with the same value in the string pool and returns a reference to it if it exists, otherwise it adds the string to the string pool and returns the reference.
6) How do you compare two strings in Java?
To compare two strings in Java, you can use the equals() method which compares the values of the strings, or the == operator which compares the references of the string objects.
7) What happens when you concatenate two strings in Java?
When you concatenate two strings in Java using the + operator, a new string object is created with the combined values of the two strings. This is because strings are immutable and cannot be modified once created.
8) How can you reverse a string in Java?
One way to reverse a string in Java is by using the reverse() method of the StringBuilder class. You can also convert the string into a character array and then swap the characters at the beginning and end of the array.
9) What is the difference between String, StringBuilder, and StringBuffer?
The main difference between String, StringBuilder, and StringBuffer is that String is immutable, StringBuilder is mutable and not thread-safe, and StringBuffer is mutable and thread-safe.
10) Is it more efficient to use StringBuilder instead of String for string concatenation?
Yes, it is more efficient to use StringBuilder instead of String for string concatenation. This is because when using StringBuilder, a new string object is not created each time, leading to better performance.
11) Can you modify a string in Java using reflection?
Yes, it is possible to modify a string in Java using reflection. However, this is not recommended as it goes against the principle of immutability and can lead to unexpected results.
12) How do you convert a string to all uppercase or lowercase in Java?
You can use the methods toUpperCase() and toLowerCase() in the String class to convert a string to all uppercase or lowercase respectively.
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13) What is string interning in Java?
String interning is the process of storing only one copy of each distinct string value in a string pool and reusing that object for all instances of the same string value. This helps in saving memory and improving performance.
14) Can a string be null in Java?
Yes, a string can be null in Java. This indicates that the string does not have a value or has been explicitly set to null.
15) What is the difference between String, StringBuffer, and StringBuilder in terms of thread-safety?
String is immutable and therefore thread-safe, StringBuffer is mutable and thread-safe, and StringBuilder is mutable but not thread-safe. This means that multiple threads can safely access and modify a StringBuffer or StringBuilder object, but not a String object.
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